New England Regional Primate Research Center
P.O. Box 9102
Southborough, MA 01772-9102
HIV-1 Entry. For HIV-1 to enter its target T-cell or macrophage, its envelope glycoprotein gp120 binds the cellular receptor CD4. This induces a conformational change in gp120 that allows it to associate with a coreceptor such as the chemokine receptor CCR5 or CXCR4. The coreceptor is actually more important than CD4; it is necessary, and in some cases sufficient, for HIV-1 to enter its target cells. Association with the coreceptor induces a dramatic conformational change in the envelope glycoprotein gp41 that allows its amino-terminus to associate with the target-cell membrane, facilitating mixing of the viral and cellular lipids and ultimately entry of the viral capsid into the cell. CCR5 is the primary coreceptor used during transmission and replication during the asymptomatic period of infection. We have studied CCR5 extensively, mapping a domain in the amino-terminus of the receptor that is critical for HIV-1 entry. This domain is rich in tyrosine and acidic residues, and we have shown that the tyrosines in this region are modified by the addition of sulfate. These sulfates are quite important for HIV-1 replication. For example, peptides based on the amino-terminus of CCR5 can inhibit HIV-1 entry only if they are sulfated, and sulfated peptides can complement the inability of a CCR5 lacking an amino-terminus to support HIV-1 entry.
The HIV-1 Antibody Response. We have shown that antibodies can mimic CCR5 in a number of ways, including by sulfating the tyrosines in their antigen-binding regions. These antibodies may be important because the virus has greater difficulty escaping from an antibody that so closely mimics its obligate receptor. We are currently investigating these antibodies, their role in controlling infection in the population of long-term non-progressing patients, and how to better elicit them. We are also using structural information derived from these antibodies to build better inhibitors of HIV-1 entry. We are committed to using recent advances in mass spectroscopy to provide a higher resolution view of the antibody response to HIV-1. We think this work will be important to developing and evaluating vaccines against HIV-1.
The SARS Receptor. Last year (2003) we identified the receptor, ACE2, necessary (and apparently sufficient) for infection of cells by the SARS virus. We have also defined a small region of the SARS-CoV S protein that functions as its receptor-binding domain. This work provides two immediate therapeutic approaches to SARS (a much easier problem than HIV-1). We are currently generating mice transgenic for ACE2, which we expect will be a useful model for testing vaccines and therapeutics. Finally, we are describing the determinants on the SARS-CoV envelope glycoprotein that permitted transmission from civet cats (likely the natural host of SARS-CoV) to humans.
Farzan M, Mirzabekov T, Kolchinsky P, Wyatt R, Cayabyab M, Gerard NP, Gerard C, Sodroski J, Choe H. Tyrosine sulfation of the amino-terminus of CCR5 facilitates HIV-1 entry. Cell 1999;96:667-76.
Farzan M, Vasilieva N, Schnitzler CE, Chung S, Robinson J, Gerard NP, Gerard C, Choe, H, Sodroski J. A tyrosine-sulfated peptide based on the N-terminus of CCR5 interacts with a CD4-enhanced epitope of the HIV-1 gp120 envelope glycoprotein and inhibits HIV-1 entry. J Biol Chem 2000 275:33516.
Farzan M, Schnitzler CE, Vasilieva N, Leung D, Kuhn J, Gerard C, Gerard NP, Choe H. Sulfated tyrosines contribute to the formation of the C5a docking site of the human C5a anaphylatoxin receptor. J Exp Med 2001 193:1059-1066.
Farzan M, Babcock GJ, Vasilieva N, Wright PL, Kiprilov E, Mirzabekov T, Choe H The role of post-translational modifications of the CXCR4 amino-terminus in SDF-1 association and HIV-1 entry. J Biol Chem 2002, 277:29484-9.
Farzan M, Chung S, Li W, Vasilieva N, Schnitzler CE, Marchione RJ, Gerard C, Gerard NP, Sodroski J, Choe H. Tyrosine-sulfated peptides functionally reconstitute a CCR5 variant lacking a critical amino-terminal region. J Biol Chem 2002, 277:40397-402.
Choe H, Li W, Wright PL, Vasilieva N, Venturi M, Huang CC, Grundner C, Zwick MB, Wang L,Rosenberg ES, Kwong PD, Burton DR, Robinson JE,Sodroski, JG, Farzan M. Tyrosine Sulfation of Human Antibodies Contributes to Recognition of the CCR5-binding Region of HIV-1 gp120. Cell 2003;114:161-70.
Li W, Moore MJ, Vasilieva N, Sui J, Wong SK, Berne MA, Somasundaran M, Sullivan JL, Luzuriaga K, Greenough TC, Choe H and Farzan M. Angiotensin-converting enzyme 2 is a functional receptor for the SARS coronavirus. Nature 2003;426:450-4.
Wong SK, Li W, Moore MJ, Choe H and Farzan M. A 193-amino-acid fragment of the SARS coronavirus S protein efficiently binds angiotensin-converting enzyme 2. J Biol Chem 2004;279:3197-201.